METHOD AND APPARATUS FOR AN I-CSCF TO ASSIGN TO A USER EQUIPMENT A S-CSCF SERVER IN AN IMS SYSTEM

A method for assigning to a terminal device (UE) a service server (SS) carried out by an IS, by any of the SSs, and by the UDB in a cooperative/corresponding manner. A "first reallocation (IS/SS/UDB) procedure" and a "second reallocation (IS/SS/UDB) procedure" are correspondingly performed within the IS, the SS and the UDB. The first reallocation procedure allows, via IS/SS/UDB processing and interactions, storing by the UDB, in relationship with at least one of the user identifiers of a UE, a mark indicating that the UE has been assigned to a replacement SS to substitute another SS that has failed. The second reallocation procedure allows, also via IS/SS/UDB processing and interactions, utilization of the mark to trigger a new SS reallocation of the UE to a SS when the UE sends a subsequent registration message.